Percutaneous angioplasty is a therapeutic medical procedure that can increase blood flow through a blood vessel. It can sometimes be used as an alternative to coronary by-pass surgery, for example. An elongated catheter having a deflated balloon at its distal end is guided through a patient's cardiovascular system to the coronary artery of the heart. The balloon is inflated to compress deposits that have accumulated along the inner walls of the coronary artery to widen the artery lumen and increase blood flow.
A known technique for positioning the balloon catheter uses an elongated guidewire that is inserted into the patient and routed through the cardiovascular system as guidewire progress is viewed on an x-ray imaging screen.
Representative prior art patents that disclose flexible, elongated guidewires are U.S. Pat. No. 4,545,390 to Leary, U.S. Pat. No. 4,538,622 to Samson et al. and U.S. Pat. No. 3,906,938 to Fleischhacker and U.S. Pat. 4,846,186 to Box et al. The Box et al. patent is incorporated herein by reference.
Occasionally, during the performance of an angioplasty procedure, the physician determines a different catheter is needed for the particular procedure. This can occur, for example, if the size of the catheter is not appropriate for the particular blood vessel blockage that is being treated.
It also may be necessary to exchange catheters if difficulty is encountered in pushing the catheter through a lesion. If a guidewire can be guided through the lesion but the catheter balloon cannot, the physician may decide to withdraw the catheter and insert a smaller diameter catheter to bridge the lesion with the smaller balloon. If the smaller balloon is successfully placed, it is inflated to create a larger passageway through the lesion and then the larger diameter catheter may be reinserted and used to widen the passageway even further. When exchanging catheters, it is important that the guidewire tip not be retracted from its position. If the guidewire is removed from the lesion, the limited passage may close due to a blood vessel spasm so that the guidewire cannot again be pushed through the lesion.
U.S. Pat. No. 4,872,941 to Taylor et al. concerns an extendable guidewire system for introducing a dilatation catheter into a cardiovascular system. The guidewire has a guidewire section and extension section with a connection for joining the two sections. The guidewire section is used for positioning the catheter within the subject, and the extension section can be used to extend the length of the guidewire for use in exchanging catheters. The structure shown in the '941 patent uses separate parts which must be assembled when an exchange of catheters is deemed appropriate.
U.S. Pat. No. 4,846,193 to Tremulis et al. concerns an extendable guidewire and method for introducing and exchanging catheters in vascular procedures such as coronary angioplasty. The guidewire has first and second interfitting sections movable between extended and retracted positions.